1. Field of the Invention
This invention relates to a process for preparing cigarette filters, for example, a cigarette filter as disclosed in Japanese Patent No. 278,071 (Patent Publication No. 5750/59). More particularly, this invention relates to a process for preparing a cigarette filter which comprises blooming a tow of cellulose acetate fibers, applying a plasticizer or the like onto the bloomed tow by spraying or other suitable means, and gathering the thus-treated bloomed tow to form a cigarette filter rod.
2. Description of the Prior Art
As preferred plasticizers for cellulose acetate fiber formed into cigarette filters, it is known to use glycerol triacetate, i.e., triacetin, and diacetates, dipropionates and dibutyrates of triethylene glycol, tetraethylene glycol and pentaethylene glycol. Since triacetin fails to give a sufficiently rapid curing rate, when triacetin is used as a plasticizer, it takes a long time to impart a prescribed hardness to the filter. Further, deformation readily occurs during the cutting operation and/or storage. Moreover, as is well known, the bitter characteristic of triacetin reduces the taste and flavor of the cigarettes. In the case of glycol esters such as triethylene glycol diacetate, it is known that the curing rate is rapid, the phenol filtering ratio is high and these characteristics scarcely change with the passage of time. However, the latter plasticizers dissolve the fibers excessively thereby to form voids by partial dissolution of the fibers. As a result, the pressure drop and the filtration efficiency are reduced. Further, it cannot be said that such plasticizers will provide a good taste or flavor.
As indicated above, a plasticizer to be used for preparing a cigarette filter composed of cellulose acetate fibers should have a curing rate which is neither too high nor too low, but rather is maintained at a suitable intermediate level, and such should provide good taste and flavor to smokers. Therefore, the suitability of plasticizers cannot be evaluated only from a consideration of a single property, such as its plasticizing activity to cellulose acetate fibers. Various studies have heretofore been made in this field, but no fully satisfactory results have been obtained yet.